1. Technical Field
The present invention relates to a light source device, an illuminating device, a backlight device and liquid crystal display device which are provided with a light-emitting element, and a display device for displaying a video image.
2. Description of Related Art
A liquid crystal display device referred to as a thin type such as a liquid crystal television includes a display unit which has, on a right side, a display surface for displaying an image and takes a shape of an almost rectangular parallelepiped, and a light source device disposed on a back side of the display unit for applying light on the display unit, and a diffusion plate and an optical sheet such as a prism sheet are provided between the light source device and the display unit.
The display unit has a liquid crystal display panel taking a shape of an almost rectangular parallelepiped. The liquid crystal display panel itself does not emit light. For this reason, an illuminating light source for displaying a video image on the display surface is required, and a backlight device is used as the illuminating light source.
As the backlight device, there are generally employed an edge light system in which a light guide is provided on a back side of a display unit and an illuminating light source is disposed on an edge side of the light guide, and a falling system in which a diffusion plate is provided on the back side of the display unit and an illuminating light source is disposed on a back side of the diffusion plate.
Referring to the edge light system of the backlight device, a cold cathode fluorescent lamp (CCFL) is provided on the edge side of the light guide and light incident from the edge of the light guide is emitted from one surface of the light guide while guiding light in the light guide (for example, see Japanese Laid-Open Patent Publication No. 2005-4200). Therefore, a luminance characteristic can be enhanced in a display device including a display surface having a comparatively small area. Referring to a display device including a display surface having a comparatively large area, however, it is hard to uniformly enhance the luminance characteristic. For this reason, in a display device such as a television which is increasingly large-sized, the backlight device of the falling system is used.
For a backlight device of a falling type, there are generally employed, as an illuminating light source, a CCFL type (for example, see Japanese Laid-Open Patent Publication No. 2008-116832) in which a plurality of cold cathode fluorescent lamps (CCFLs) having electrodes on both ends and taking a shape of a straight pipe or an almost U shape are juxtaposed on a back side of the diffusion plate, and an LED type (for example, see Japanese Laid-Open Patent Publication No. 2007-73300, Japanese Laid-Open Patent Publication No. 2008-305940, Japanese Laid-Open Patent Publication No. 2007-322697) in which a plurality of light-emitting diodes (LEDs) are juxtaposed on a back side of the diffusion plate.
The backlight device of the CCFL type includes a plurality of cold cathode fluorescent lamps juxtaposed vertically apart from each other in a direction along a surface of a diffusion plate, a support case for accommodating and supporting the cold cathode fluorescent lamps, an inverter circuit board for emitting light from the cold cathode fluorescent lamps, and a cover for covering the inverter circuit board.
However, the backlight device of the CCFL type requires high voltage components such as, for example, the inverter circuit board for discharging the cold cathode fluorescent lamp, the electrodes on the both ends of the cold cathode fluorescent lamp and the like, and it is necessary to maintain a comparatively long insulating distance around the high voltage components. Therefore, the high voltage components hinder a longitudinal thickness from being reduced. For this reason, there is a tendency that a backlight device of an LED type which has no high voltage component, does not need to maintain a comparatively long insulating distance and is more advantageous to reduce a longitudinal thickness than the backlight device of the CCFL type is employed for a recent display device.
Moreover, the cold cathode fluorescent lamp is formed in a length provided over both ends in a transverse direction of the diffusion plate. For this reason, it is impossible to control a lighting operation of the cold cathode fluorescent lamp in a fine area. Furthermore, a high-speed flashing control for suppressing an animation blur or the like is more disadvantageous as compared with the LED type. In addition, power consumption is increased because the cold cathode fluorescent lamps are turned ON at a high voltage. Consequently, a heat value is also increased when the cold cathode fluorescent lamps are ON. Therefore, it is advantageous to employ the backlight device of the LED type which can easily carry out a control in a fine area and a high-speed flashing control, and furthermore, can lessen a power consumption and a heat value more greatly than the backlight device of the CCFL type.
The backlight device of the LED type includes a plurality of light-emitting diode substrates having one surface on which a plurality of light-emitting diodes are mounted, a support case for accommodating and supporting the light-emitting diode substrates, and a power board for emitting light from the light-emitting diodes.
The applicant of the present invention developed a backlight device of an LED type including a plurality of light-emitting diode substrates, each of which has a plurality of light-emitting diodes mounted on one surface and takes a shape of a strip connected in a line, a support case for accommodating and supporting the light-emitting diode substrates in a plurality of lines apart from each other in a vertical direction, a shaft member such as a rivet for fixing both ends of the light-emitting diode substrate, a connector for connecting the light-emitting diode substrates which are adjacent to each other, a plurality of lenses attached to one surface of the light-emitting diode substrate opposite to the light-emitting diode for diffusing light emitted from the light-emitting diode, a reflection sheet mounted on one of the surfaces of the light-emitting diode substrate for reflecting the light diffused by the lens, and a support pin for suppressing a flexure of the diffusion plate.
The backlight device of the LED type is assembled in accordance with the following steps (1) to (5).
(1) The support case is put flatly on a working table with an open side turned upward, and the light-emitting diode substrates which are adjacent to each other in a transverse direction are juxtaposed in a plurality of lines in the support case.
(2) The light-emitting diode substrates which are adjacent to each other are connected to each other through the connector, and a power connecting connector is connected to the end of the light-emitting diode substrate on an end side.
(3) Both ends of the light-emitting diode substrates which are juxtaposed are fixed to the support case by means of the shaft member such as a rivet.
(4) The reflection sheet is mounted on one of the surfaces of the light-emitting diode substrate.
(5) The support pins are attached to the support case from the reflection sheet side.
The support case is formed by a metal plate and has a flat plate-shaped plate portion taking a square shape, a frame portion linked to a peripheral edge of the plate portion and having one of sides opened, and four collar pieces linked to an outer edge of the frame portion. The plate portion is provided with a first mounting hole in an opposite position to the both ends of the light-emitting diode substrates which are juxtaposed, and a second mounting hole in a position in which the support pin is to be disposed.
The light-emitting diode substrate takes a shape of a strip in which a circuit portion is provided on one surface, the light-emitting diode and a lens are mounted on the surface and a connecting portion is provided on one surface of both ends, and a through hole corresponding to the first mounting hole is provided on the both ends.
The light-emitting diode is formed in such a manner that an emitted light concentrates within a predetermined angle based on an optical axis from a front of the light-emitting diode.
The lens is opposed to a top of the light-emitting diode apart from each other, and takes a shape of a thick disk having a hemispherical recess portion for diffusing light applied from the light-emitting diode in all directions.
The reflection sheet takes a square shape corresponding to the plate portion of the support case and has a structure in which a first hole taking a larger shape than the lens is provided in an opposed position to the lens and a second hole taking a larger shape than the connector is provided in an opposed position to the connector, the lens is provided in the first hole and the connector is provided in the second hole when the reflection sheet is mounted over the surface of the light-emitting diode substrate, and a thermal expansion of the reflection sheet through the light-emitting diode can be absorbed.
Japanese Laid-Open Patent Publication No. 2007-73300 describes that a mark is printed on a circuit board to enable an easy confirmation of an orientation of the circuit board. A plurality of circuit boards which take a rectangular shape and are to be juxtaposed in a matrix and attached to an attaching member are disposed in such a manner that a longitudinal direction is coincident with a transverse direction. A light-emitting portion (for example, a light-emitting diode) is mounted on each of the circuit boards. Furthermore, each of the circuit boards has a first connecting portion (for example, a male connecting portion) mounted on a right end and a second connecting portion (in this case, a female connecting portion) mounted on a left end.
In the adjacent circuit boards to each other in the transverse direction, the first connecting portion of the circuit board disposed on a left side and the second connecting portion of the circuit board disposed on a right side are connected to each other through a connector for bridging the connecting portions.
When the circuit board is to be attached to the attaching member, an operator needs to confirm an orientation in the transverse direction of the circuit board (which will be hereinafter referred to as the orientation of the circuit board). However, the first connecting portion and the second connecting portion have similar shapes to each other. Therefore, it is hard to confirm the orientation of the circuit board by setting a difference in the shape between the first and second connecting portions as a clue.
If the circuit board is attached to the attaching member in a reverse orientation, the circuit boards which are adjacent to each other cannot be connected to each other through the connector. In the case in which a work for attaching the circuit board is started without a recognition of the reverse orientation of the circuit board, moreover, it is necessary to carry out a work for reattaching the circuit board in a correct orientation again even if an error is recognized before the circuit board is ended to be attached. As a result, an efficiency of the attaching work is reduced. For this reason, in the Japanese Laid-Open Patent Publication No. 2007-73300, it is possible to easily confirm the orientation of the circuit board by printing a mark on the circuit board.
Japanese Laid-Open Patent Publication No. 2008-305940 describes a backlight device having a structure in which a plurality of LED substrates (element substrates) are used, each of which has a plurality of LEDs (solid state light-emitting elements) arranged and mounted on one face vertically and transversely, and the LED substrates are attached onto a chassis formed to take a shape of a shallow box and a large number of LEDs are disposed uniformly inside of the chassis. Each of the LEDs mounted on the LED substrate is covered with a light diffusing lens (cap) and a bottom plate of the chassis provided with the LED is covered wholly with a reflection sheet having an excellent light reflectance, and light emitted from each of the LEDs is diffused by each len, and furthermore, is reflected by the reflection sheet to carry out a uniform light application over a whole back face of a liquid crystal display panel.
Japanese Laid-Open Patent Publication No. 2007-322697 describes a backlight device having a structure in which a support pin is provided in such a manner that a base end is attached to an LED substrate in a penetration through a reflection sheet and a tip portion is protruded from the LED substrate, and an optical sheet is supported by the support pin to hold an opposed interval between the optical sheet and the LED substrate.
Japanese Laid-Open Patent Publication No. 2005-4200 describes a backlight device of an edge light type in which a light source is disposed in both side portions of a support plate for supporting a liquid crystal display panel and a light guide at one face, driving operations of the liquid crystal display panel and the light source are controlled by a circuit board provided on the other face of the support plate, and a transmission line (a conductor) connected to the circuit board is connected to the liquid crystal display panel and the light source via a through hole provided on the support plate to transmit a driving signal to the liquid crystal display panel and the light source. The support plate is housed in a thin housing and the conductor needs to be accommodated in a limited space. Therefore, a groove is formed in an edge portion of a housing container (a support plate) for housing the light source, the display panel and the like, and a plurality of conductors passing the through hole are housed in the groove.